Synthesis of branched poly(methyl methacrylate)s via controlled/living polymerisations exploiting ethylene glycol dimethacrylate as branching agent

Highly Branched Polydimethylacrylamide Copolymers as Functional Biomaterials

Controlled radical polymerization of vinyl monomers with multivinyl cross-linkers leads to the synthesis of highly branched polymers with controlled spatial density of functional chain ends. The resulting polymers synthesized in this manner have large dispersities resulting from a mixture of unreacted primary chains, low molecular weight branched species, and high molecular weight highly branched species. Through the use of fractional precipitation, we present a synthetic route to high molecular weight highly branched polymers that are absent of low molecular weight species and that contain reactivity toward amines for controlled postpolymerization modification. The controlled spatial density of functional moieties on these high molecular weight macromolecular constructs enable new functional biomaterials with the potential for application in regenerative medicine, immunoengineering, imaging, and controlled drug delivery.

Highly branched polymethacrylates prepared efficiently: brancher-directed topology and application performance

A series of highly oil-soluble and branched polymethacrylates are prepared via ATRcP of 2-ethylhexyl methacrylate and divinyl brancher with high efficiency, focusing on the brancher effect on the structure-performance of the polymers.

Impact of multi-vinyl taxogen dimensions on high molecular weight soluble polymer synthesis using transfer-dominated branching radical telomerisation

The creation of branched polymers by TBRT is influenced by the molecular dimensions of the polymerising species. A mechanistic understanding is presented that includes a radical lifetime sphere model that is unique to telomerisation conditions used.

Universal Scaling Behavior during Network Formation in Controlled Radical Polymerizations

Despite the ubiquity of branched and network polymers in biological, electronic, and rheological applications, it remains difficult to predict the network structure arising from polymerization of vinyl and multivinyl monomers. While controlled radical polymerization (CRP) techniques afford modularity and control in the synthesis of (hyper)branched polymers, a unifying understanding of network formation providing grounded predictive power is still lacking. A current limitation is the inability to predict the number and weight average molecular weights that arise during the synthesis of (hyper)branched polymers using CRP. This study addresses this literature gap through first building intuition via a growth boundary analysis on how certain environmental cues (concentration, monomer choice, and cross-linker choice) affect the cross-link efficiency during network formation through experimental gel point measurements. We then demonstrate, through experimental gel point normalization, universal scaling behavior of molecular weights in the synthesis of branched polymers corroborated by previous literature experiments. Moreover, the normalization employed in this analysis reveals trends in the macroscopic mechanical properties of networks synthesized using CRP techniques. Gel point normalization employed in this analysis both enables a polymer chemist to target specific number and weight average molecular weights of (hyper)branched polymers using CRP and demonstrates the utility of CRP for gel synthesis.

Comparison of Thermoresponsive Hydrogels Synthesized by Conventional Free Radical and RAFT Polymerization

We compared the influence of the polymerization mechanism onto the physical characteristics of thermoresponsive hydrogels. The Poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were successfully synthesized using reversible addition-fragmentation chain-transfer (RAFT) and free radical polymerization (FRP). The gels were prepared while using different crosslinker feed and monomer concentration. The swelling, dye release, and hydrolytic stability of the gels were investigated in water, or in representative komostrope and chaotrope salt solutions at room temperature and at 37 °C. It was found that the swelling ratio (SR) of the RAFT gels was significantly higher than that of the FRP gels; however, an increased crosslinking density resulted in a decrease of the SR of the RAFT gels as compared to the corresponding gels that are made by FRP, which indicates the limitation of the cross-linking efficiency that is attained in RAFT polymerization. Additionally, an increased monomer concentration decreased the SR of the RAFT gels, whereas a similar SR was observed for the FRP gels. However, the SR of both RAFT and FRP gels in NaSCN and Na₂SO₄ solutions were similar. Finally, the rate of dye release was significantly slower from the RAFT gels than the FRP gels and the hydrolytic stability of the RAFT gels was lower than that of FRP gels in water, but maintained similar stability in Na₂SO₄ and NaSCN solutions.

Expanding the monomer scope of linear and branched vinyl polymerisations via copper-catalysed reversible-deactivation radical polymerisation of hydrophobic methacrylates using anhydrous alcohol solvents

The use of anhydrous alcohols for Cu-catalysed reversible-deactivation radical polymerisation of a wide range of hydrophobic methacrylates has been explored in detail.

Branched poly (trimethylphosphonium ethylacrylate-co-PEGA) by RAFT: alternative to cationic polyammoniums for nucleic acid complexation

Cationic and highly branched poly (trimethylphosphonium ethylacrylate-co-poly (ethylene glycol) acrylate) (p (TMPEA-co-PEGA)), and its ammonium equivalent, have been synthesised from post-polymerisation modification of a poly (bromo ethylacrylate-co-poly (ethylene glycol) acrylate) (p (BEA-co-PEGA)) precursor polymer produced using reversible addition fragmentation chain transfer (RAFT) polymerisation. The cationic polymers were evaluated for their ability to complex nucleic acids, their in vitro cytotoxicity and their GFP pDNA transfection efficiency. The results show RAFT copolymerisation of BEA and PEGA is a simple route to polyphosphoniums showing reduced cytotoxicities and higher transfection efficiencies than their polyammonium alternatives.

Synthesis and characterisation of highly branched polyisoprene: exploiting the “Strathclyde route” in anionic polymerisation

This work aimed at developing a synthetic route towards highly branched poly(isoprene) from commercially available raw materials, in good yield and devoid of microgelation, i.e., to prepare a completely soluble polymer via the versatile technique anionic polymerisation. The polymerisations were conducted under high vacuum conditions using sec-butyllithium as initiator at 50 °C in toluene. Toluene served both as a solvent and as a chain-transfer agent. The polar modifier used was tetramethylethylenediamine (TMEDA), and a commercial mixture of divinylbenzene (DVB) was employed as the branching agent for the “living” poly(isoprenyl)lithium anions. The nature of the reaction was studied on the TMEDA/Li ratio as well as the DVB/Li ratio. The obtained branched polymers were characterised by triple detection size exclusion chromatography (SEC), proton nuclear magnetic resonance spectroscopy (¹H NMR), differential scanning calorimetry (DSC) and melt rheology. Broad molecular weight distributions have been obtained for the highly branched polymer products. ¹H NMR spectroscopy reveals the dominance of 3,4-polyisoprene microstructure. It was found that the complex viscosities and dynamic moduli of the branched samples were much lower compared to their linear counterparts. The results conform with earlier findings by the “Strathclyde team” for radical polymerisation systems. This methodology has the potential of providing soluble branched vinyl polymers at low cost using the readily available raw materials.

Copolymerisation of isoprene and divinylbenzene was achieved in toluene via anionic chain transfer polymerization to yield highly branched polymers with good solution and rheological properties.

Cationic branched polymers for cellular delivery of negatively charged cargo

Receptor-independent cellular uptake of small molecule therapeutics is limited by their physical interaction with the negatively charged surface of cellular membranes. Passive diffusion through the hydrophobic membrane bilayer follows this process. Unless specific carriers exist in the biological membrane, such interactions limit therapeutics to those that are hydrophobic with modest positive charge at physiological pH. Small negatively charged molecules are therefore not efficient as therapeutics. To enable delivery of such molecules into eukaryotic cells, cationic branched polymers with tetraalkylammonium pendant groups were synthesized by copolymerization of a functional monomer (glycidyl methacrylate) with degradable and non-degradable divinyl crosslinkers in the presence of an efficient chain transfer agent, CBr4, followed by reaction of the multiple pendant epoxide groups and most of the alkyl bromide chain ends with amines. Cationic branched polymers with covalently attached fluorescent labels entered human cancerous and non-cancerous cells. The non-labeled analogues were able to carry anionic cargo (carboxyfluorescein) into the cells, while no uptake was observed in the absence of the cationic carriers. Most of the polymers were not significantly toxic at the concentrations used. This pilot study showed that cellular uptake of anionic small molecules can be promoted even in the absence of natural uptake mechanisms.

Preparation and Properties of Branched Polystyrene through Radical Suspension Polymerization

Radical solvent-free suspension polymerization of styrene with 3-mercapto hexyl-methacrylate (MHM) as the branching monomer has been carried out using 2,2'-azobisisobutyronitrile (AIBN) as the initiator to prepare branched polymer beads of high purity. The molecular weight and branching structure of the polymers have been characterized by triple detection size exclusion chromatography (TD-SEC), proton nuclear magnetic resonance spectroscopy (¹H-NMR), and Fourier transform infrared spectroscopy (FTIR). The glass transition temperature and rheological properties have been measured by using differential scanning calorimetry (DSC) and rotational rheometry. At mole ratios of MHM to AIBN less than 1.0, gelation was successfully avoided and branched polystyrene beads were prepared in the absence of any solvent. Branched polystyrene has a relatively higher molecular weight and narrower polydispersity (Mw.MALLS = 1,036,000 g·mol-1, Mw/Mn = 7.76) than those obtained in solution polymerization. Compared with their linear analogues, lower glass transition temperature and decreased chain entanglement were observed in the presently obtained branched polystyrene because of the effects of branching.

Synthesis of highly branched polymers by reversible complexation-mediated copolymerization of vinyl and divinyl monomers

Here, we report the reversible complexation-mediated copolymerization (RCMcP) of vinyl and divinyl monomers for the synthesis of highly branched polymers.

Radical polymerization in the presence of a peroxide monomer: an approach to branched vinyl polymers

In this paper, we report radical polymerization in the presence of a peroxide monomer for the preparation of branched vinyl polymers.

Doubly-responsive hyperbranched polymers and core-crosslinked star polymers with tunable reversibility

Thermo- and redox-responsive hyperbranched copolymers were prepared by statistical copolymerization of N-isopropylacrylamide (NIPAM) and N,N′-bis(acryloyl)cystamine (BAC) by reversible addition–fragmentation chain transfer (RAFT) polymerization.

A rapid crosslinking injectable hydrogel for stem cell delivery, from multifunctional hyperbranched polymers via RAFT homopolymerization of PEGDA

A novel injectable hydrogel for stem cell delivery was prepared from multifunctional hyperbranched polyPEGDA and thiolated hyaluronic acid.

Monodisperse highly cross-linked “living” microspheres prepared via photoinitiated RAFT dispersion polymerization

Monodisperse highly Cross-linked “Living” microspheres were synthesized via photoinitiated RAFT dispersion polymerization of MMA using a bifunctional monomer or a trifunctional monomer as the cross-linker.

RAFT-mediated control of nanogel structure and reactivity: chemical, physical and mechanical properties of monomer-dispersed nanogel compositions

OBJECTIVE

This study examines how nanogel structure correlates with photopolymerization and key polymer properties upon addition of nanogels with latent reactivity into a monomer dispersant to produce polymer/polymer composites.

METHODS

Two nanogels that retained RAFT functionality based on the synthetic approach were prepared to have different branching densities. These reactive nanogels were dispersed in triethylene glycol dimethacrylate at 0-40 wt%. Reaction kinetics, volumetric shrinkage and shrinkage stress associated with the photopolymerization of nanogel-modified formulations were measured in real time with mechanical properties of the polymers also evaluated. The basic structure of RAFT-derived nanogel particles was examined by the preparation of a separate nanogel constructed with degradable disulfide crosslinking groups. The model nanogel molecular weight and polydispersity were compared before and after degradation.

RESULTS

Despite the controlled radical synthetic approach, the nanogels, which are composed of multiple interconnected, short primary chains, presented relatively high polydispersity. Through addition of the reactive nanogels to a monomer that both infiltrates and disperses the nanogels, the photopolymerization rate was moderately reduced with the increase of nanogel loading levels. Volumetric shrinkage decreased proportionally with nanogel concentration; however, a greater than proportional reduction of polymerization-induced stress was observed. Mechanical properties, such as flexural strength, storage modulus were maintained at the same levels as the control resin for nanogel systems up to 40 wt%.

SIGNIFICANCE

This study demonstrated that beyond the use of RAFT functionality to produce discrete nano-polymeric structures, the residual chain end groups are important to maintain reactivity and mechanical properties of nanogel-modified resin materials.

Facile one-spot synthesis of highly branched polycaprolactone

First solvent-free synthesis of degradable/bioresorbable, highly branched polymers via Sn(Oct)₂ controlled ROP containing di-functional lactones to near quantitative conversion.

Employing exchange reactions involving hypervalent iodine compounds for the direct synthesis of azide-containing linear and branched polymers

Azide-containing polymers were prepared by one-pot polymerizations initiated by azide radicals produced by ligand exchange reactions involving hypervalent iodine(iii) compounds.

Controlled multi-vinyl monomer homopolymerization through vinyl oligomer combination as a universal approach to hyperbranched architectures

The three-dimensional structures of hyperbranched materials have made them attractive in many important applications. However, the preparation of hyperbranched materials remains challenging. The hyperbranched materials from addition polymerization have gained attention, but are still confined to only a low level of branching and often low yield. Moreover, the complication of synthesis only allows a few specialized monomers and inimers to be used. Here we report a 'Vinyl Oligomer Combination' strategy; a versatile approach that overcomes these difficulties and allows facile synthesis of highly branched polymeric materials from readily available multi-vinyl monomers, which have long been considered as formidable starting materials in addition polymerization. We report the alteration of the growth manner of polymerization by controlling the kinetic chain length, together with the manipulation of chain growth conditions, to achieve veritable hyperbranched materials, which possess nearly 70% branch ratios as well as numerous vinyl functional groups.